1. Field of the Invention
This invention relates to a 3-D camera system and to a method for shifting the grating shadow used in creating three-dimensional images.
2. Description of the Prior Art
Using Phase Shifting Interferometry to create a three dimensional bit-map image of an object is well known in the art, and typically includes a light source, lens and a grating which are used to project an image of the grating onto the object being imaged. This method of creating a three dimensional image requires the taking of three or more different images of the object. The projected pattern in each image is shifted to create three images of the object with unique light patterns projected on the object. By knowing what the shift is between images, and using trigonometric equations based on the distances between the light source, lens, grating, object, and imaging system, a processor creates a three dimensional bit-map of the object.
The most common way of shifting the projected pattern from one image to the other has been to move the grating. U.S. Pat. No. 5,646,733 to Bieman, and U.S. Pat. No. 4,212,073 to Balasubramanian disclose this method of shifting the grating pattern. This can be achieved by attaching the grating to a servo motor or some other suitable means to move the grating. Other methods have been utilized such as projecting the light through clear substrates having multiple bands of liquid crystal, as disclosed in U.S. Pat. No. 5,581,352 to Zeien. The bands of liquid crystal are selectively activated to create varying shadow patterns as the light is projected through them. Another method involves the use of a grating in combination with a clear glass plate, as disclosed in U.S. Pat. No. 5,471,308 to Zeien. The glass plate is rotated on an axis by way of a servo motor. The result is to cause the image of the grating to shift as it is projected through the lens. Although simple enough to achieve, these methods have historically made three dimensional imaging systems costly. The additional equipment needed to facilitate the movement of components in the systems described above also makes the systems bulky, and not appropriate for applications where the system must be compact and mobile. Waiting for the mechanical movement to shift the grating image also adds time to the process.